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691.
We define a sequence of real functions which coincide with Li'scoefficients at one and which allow us to extend Li's criterionfor the Riemann Hypothesis to yield a necessary and sufficientcondition for the existence of zero-free strips inside the criticalstrip 0 < R(z) < 1. We study some of the properties ofthese functions, including their oscillatory behaviour. 相似文献
692.
Experimental evidence have been suggesting that the toxicity of metals may involve inflammatory processes, with subsequent sustained overproduction of pro-oxidant reactive species, leading to indirect toxic effects, namely genotoxicity. Neutrophils, as important mediators of the innate defence systems, may have a hitherto not known role on these metal-induced adverse effects. Thus, the aim of the present study was to evaluate the putative activation of human neutrophils' oxidative burst by two groups of metals, the first group being able to undergo redox-cycling reactions (iron, copper, chromium and cobalt), whilst the primary route for the toxicity of the second group is not dependent on redox reactions (mercury and cadmium). The generation of reactive oxygen species (ROS) by metal-stimulated neutrophils was measured using the chemiluminometric probe luminol. Appropriate scavengers and metabolizing enzymes were subsequently used to identify the reactive species produced. The modulatory effects of metals on phorbol myristate acetate (PMA)-activated neutrophils were also studied. To evaluate the contribution of protein kinase C (PKC) on metal stimulatory effect, we used the specific inhibitor of PKC Gö6983. The obtained results showed that, in the present experimental conditions, only Cd (II) has the ability to stimulate the production of superoxide radical (O2−), hydrogen peroxide (H2O2), and hypochlorous acid (HOCl) in isolated human neutrophils. The same metal showed a synergistic effect with PMA. It was also demonstrated that Cd (II) induces neutrophils' oxidative burst mainly via activation of PKC, precluding a significant contribution of other cellular pathways for ROS generation mediated by this metal. These observations indicate that the sustained activation of human neutrophils may contribute for the long term adverse effects on human health mediated by Cd (II). 相似文献
693.
E. Andrade M. J. Madruga I. Bobos M. I. Paiva F. Maia A. Mateus R. Trindade M. C. Freitas M. A. Gonçalves 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(3):777-783
This paper describes the development of a separation method for americium from the effluents emanating from anion exchange
column, used for the recovery of plutonium from analytical waste solutions. The waste contained uranium, sodium, calcium and
iron as the major impurities as estimated by ICP-AES method. ~99% pure americium was obtained by three separation steps using
solvent extraction and extraction chromatography techniques. In the first step, uranium was quantitatively separated by giving
five contacts of equal volumes of 30% TBP in n-dodecane. Fe and Na were separated in the next step using 0.1 M TODGA + 0.5 M DHOA as the extractant. In the last step, Am
was separated from the co-extracted Ca (about 76%) using CMPO loaded extraction chromatographic column. The overall recovery
was >80% with decontamination factor (D.F.) from the impurities being >3000 while the purity of the product was 99%. 相似文献
694.
Soraya Alves de Morais Crislene Rodrigues da Silva Morais Petr?nio Filgueiras de Athayde Filho B. Freitas Lira Railda Shelsea Taveira Rocha do Nascimento 《Journal of Thermal Analysis and Calorimetry》2009,97(2):437-441
The mesoionic compounds are pentagonal heterocyclic betaines with their potential use mainly in the pharmacology field due
to the diversity of their biological activities. Their exceptional electric properties lead the compounds to be investigated
in the field such as the nonlinear optical devices. In this study, five mesoionic compounds of the 1,3-thiazole-5-thiolate
system had been synthesized from amino acids derived from glycine through 1,3-dipolar cycloaddition/cycloreversion reaction.
The compounds were characterized by the use of infrared spectrometry, thermogravimetry and differential scanning calorimetry
techniques. Thermal stability of each structure was determined and characterized by the kinetic study of the thermal decomposition
by non-isothermal thermogravimetry. The DSC curves for MI-1, MI-2, MI-3, MI-4, and MI-5 demonstrated their fusion and subsequent
decomposition with the exception of MI-3, which presented only decomposition stages. The kinetic models that better described
the thermal decomposition mechanism of the mesoionic compounds achieved by the non-isothermal methods were R1, R2 and R3 (based
on the geometric models). 相似文献
695.
Rafael O. da Silva Tiago G. Conti André F. de Moura Prof. Dr. Daniel G. Stroppa Dr. Luiz C. G. Freitas Prof. Dr. Caue Ribeiro Dr. Emerson R. Camargo Elson Longo Prof. Dr. Edson R. Leite Prof. Dr. 《Chemphyschem》2009,10(5):841-846
The right mix : SnO2:Sb nanocrystals (NCs) can be solubilized into organic solvents with a suitable solvent/surfactant combination to achieve a stable colloid (see picture). A single synthesis route and different solvent/amphiphilic molecule pairs are used to obtain soluble NC colloids, instead of requiring several syntheses to obtain soluble NCs in different solvents.
696.
A. Freitas S. Azevedo M. Machado J. R. Kaschny 《Applied Physics A: Materials Science & Processing》2012,108(1):185-193
In this work, we apply first-principles methods to investigate the stability and electronic structure of BC4N nanostructures which were constructed from hexagonal graphite layers where substitutional nitrogen and boron atoms are placed at specific sites. These layers were rolled up to form zigzag and armchair nanotubes, with diameters varying from 7 to 12 Å, or cut and bent to form nanocones, with 60° and 120° disclination angles. The calculation results indicate that the most stable structures are the ones which maximize the number of B–N and C–C bonds. It is found that the zigzag nanotubes are more stable than the armchair ones, where the strain energy decreases with increasing tube diameter D, following a 1/D 2 law. The results show that the 60° disclination nanocones are the most stable ones. Additionally, the calculated electronic properties indicate a semiconducting behavior for all calculated structures, which is intermediate to the typical behaviors found for hexagonal boron nitride and graphene. 相似文献
697.
698.
A Z Milioni J V G de Avellar T N Rabello G M de Freitas 《The Journal of the Operational Research Society》2011,62(6):1029-1037
This paper addresses the problem of assigning shares of a new total fixed output to a group of decision making units (DMUs) using data envelopment analysis (DEA), by assuming the existence of a predefined hyperbolic locus of points that characterizes the DEA frontier. The problem of redistributing an already existing output is then addressed, where the total value of this output may vary, so that no DMU is required to decrease its current output value in the new distribution. 相似文献
699.
Pore Network Simulation of Evaporation of a Binary Liquid from a Capillary Porous Medium 总被引:2,自引:0,他引:2
A pore-network model of evaporation of a binary liquid mixture into a ternary gas phase is developed. The model is applied to study the influence of surface tension gradients induced by composition variations of the liquid on the phase distribution within a capillary porous medium. Numerical simulations based on the proposed model show that the surface tension gradients lead to the accumulation of liquid near the open edge of the network. This surface tension gradient effect is only significant for weakly disordered porous media. 相似文献
700.